Fleet arena is a million times easier than squad arena, for the sole reason that ships don't have mods. In squad you're always going to be overshadowed by that one lucky dingdong who somehow ended up with a set of 30 perfect mods that make his squad just utterly untouchable.
In fleet the playing field is pretty much level - you improve your ships by improving the pilots, but once they're fully G12'd and 6e modded, that's it, they don't get any better. So you don't have that one guy that just completely dominates despite running the same team as you.
Also, most people seem to really, really hate ships for some reason (I don't get it, I love them) so the competition tends to not be as fierce for top spots.